[CH2:1]([O:8][CH2:9][C@@H:10]([C:19]([OH:21])=O)[NH:11][C:12]([O:14][C:15]([CH3:18])([CH3:17])[CH3:16])=[O:13])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.Cl.[CH3:23][NH:24][O:25][CH3:26].CN1CCOCC1>C(Cl)Cl>[CH2:1]([O:8][CH2:9][C@@H:10]([C:19]([N:24]([O:25][CH3:26])[CH3:23])=[O:21])[NH:11][C:12]([O:14][C:15]([CH3:16])([CH3:17])[CH3:18])=[O:13])[C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=1To a solution of O-benzyl-N-(tert-butoxycarbonyl)serine (5.9 g, 20.0 mmol) in CH2Cl2 (20 mL) was added N,O-dimethylhydroxylamine hydrochloride (1.95 g, 20.0 mmol) followed by N-methylmorpholine (2.20 mL, 19.98 mmol). The mixture was cooled to 0° C. and treated with a 1 M solution of N,N-dicyclohexylcarbodiimide in CH2Cl2 (20.0 mL, 20.0 mmol). The mixture was allowed to warm to ambient temperature while stirring under inert atmosphere for 18 h. The mixture was filtered, washing the solid residue with excess CH2Cl2, and the filtrate was concentrated in vacuo. The resulting oil was suspended in EtOAc, stirred for 20 min, and filtered once more, washing with EtOAc. The filtrate was concentrated to an orange oil which was purified by silica gel chromatography (20% to 60% EtOAc/hexanes) to afford the title compound as a colorless oil. 1H NMR (500 MHz, CDCl3) δ 7.35-7.25 (m, 5H), 5.44 (d, J=8.4 Hz, 1H), 4.88 (d, J=3.2 Hz, 1H), 4.53 (dd, J=12.4, 28.8 Hz, 2H), 3.71 (s, 3H), 3.69-3.64 (m, 2H), 3.21 (s, 3H), 1.44 (s, 9H). ES MS (M+1−100, for loss of BOC group)=239.2.
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